Signal rectifier circuit



April 29, 1941. s. HUNT SIGNAL RECTIFIER CIRCUII Filed April 15, 1939CUT-OFF BIAS /Q I E AMPLIFIER 7US/GNAI. GRIDS OF PRIOR TUBES DETECTORbub:

l E AMPLIFIER TO I. E NETWORK INVEN TOR. SEYMOUR HUNT 1 4M ATTORNEY.

Patented Apr. 29, 1941 SIGNAL RECTIFIER CIRCUIT Seymour Hunt, JacksonHeights, N. Y., assignor to Radio Corporation of America, a corporationof Delaware Application April 15, 1939, Serial No. 268,078

11 Claims. My present invention relates to signal rectifier circuits,and more particularly to signal detectors,

of the carrier degeneration type.

It is well known that the employing a tuned input circuit, in serieswith a load impedance furnishing audio and gain control voltages, hascertain disadvantages, The diode will handle 100% modulated signals whenthe ratio of the alternating current to direct current loads is equal tounity. The direct current load of the diode rectifier circuit is theload resistor; the alternating current load is the load resistor inparallel with all of the automatic volume control grid resistors, theaudio volume control potentiometer and the like. A small value isrequired for the magnitude of the load resistor so that the alternatingcurrent load has small shunting effect. However, a small value of loadresistor increases the loading of the tuned input circuit feeding thediode. Hence, the designer is forced to choose a low value of loadresistor with good modulation capability and heavy loading producing lowgain and poor selectivity of the amplifier feeding the diode; or a highvalue of load resistor for a reduction of the input loading with reducedmodulation capability. Additionally, the

diode itself loads the tuned circuits feeding it with the result thatthe selectivity and gain of the amplifier stage feeding the diode arereduced. Again, it is difficult automatically to control the gain of thepro-diode amplifier with the control voltage derived from the diodedetector.

It may be stated that it is one of the main objects of my presentinvention to provide a diode detector circuit which utilizes a driverstage to feed signal energy thereto, and the driver stage beingdegenerative for the carrier whereby the diode detector may utilize aresistor load of relatively small magnitude so that the diode is capableof handling 100% modulated signals without regard to any loading effecton the tuned circuits feeding the diode detector.

Another important object of this invention is to provide a signalrectification network of the diode type, and the signal input circuit ofthe diode being provided in the cathode circuit of a stage constructedto function as a carrier degenerative signal transmission tube.

Another object of my invention is to provide a detector which isdegenerative at the carrier, and whose cathode has an auxiliary anodeassociated therewith to provide a signal rectifier network for producingautomatic volume control voltage. Still another object of the inventionis to provide a receiving system in which the detector tube usual diodedetector,

iii

has its signal grid biased substantially to cut-off, and wherein anauxiliary anode is associated with the detector cathode to provide anautomatic volume control voltage source; the signal input circuit of thediode, which comprises a cathode and an auxiliary anode, being arrangedin the detector cathode circuit and being tuned to the signal carrier.

Still other objects of the invention are to improve generallythe-efiiciency of operation of the diode detector circuits and moreespecially to provide a diode rectifier which is supplied with signalsfrom a carrier degenerative signal transmission tube, the latterarrangement being economically constructed and assembled in radioreceivers.

In the drawing:

Fig. 1 illustrates an the invention;

Fig. 2 illustrates a modification of the invention.

Referring now to the accompanying drawing, wherein like referencecharacters in the different figures designate similar circuit elements,it is asarrangement embodying sumed' that the receiving system shown inFig. 1

is of the superheterodyne type For example, the numeral I may designatethe intermediate frequency resonant output circuit of the intermediatefrequency amplifier; it being understood that the intermediate frequencycan be chosen from a frequency range of to 450 kc. The rereceiveritself, of course, can be of the type used in the broadcast range of 550to 1500 kc., although the invention is equally applicable to receiversof the multi-range type. Of course, the intermediate frequency amplifier(which is not shown to preserve simplicity of the disclosure) may be preceded by the usual converter network, and one or more radio frequencyamplifiers may precede the converter.

The circuit 1 which is the tuned primary circuit of the intermediatefrequency transformer T, and the tuned secondary 2 thereof, may beresonated to the operating intermediate frequency. The numeral 3 denotesan intermediate frequency amplifier which may be inserted, if desired,between circuit 2 and the transformer T1. Amplifier 3 is of usualconstruction, and includes the usual selfbiasing network 4. The primarycircuit 5 of transformer T1 is resonated to the intermediate frequency,and this is also true of the tuned secondary circuit 6. The tube 1 is atube of the multifunction type, and may, for example, be a tube of theSQ? or 6R7 type. In general, these tubes are of the duplex diode-triodetype, and hence tube 1 has been denoted as comprising a cathode 8, a

signal grid 9 and a plate Hi. The numeral denotes the auxiliary diodeanode to be used for diode detection, and it is to be understood thatnumeral ll actually consists of the two auxiliary anodes strappedtogether, and which is shown as a single anode in order to simplify thedrawing.

The Cathode 8 provides independent electron streams to auxiliary anode Hand to plate It]. The cathode 8 is connected to ground through animpedance which comprises the coil l2, the latter being shunted bycondenser 13 for resonating the coil to the operating intermediatefrequency. The signal grid 9 is connected to the tuned input circuit Band a biasing voltage source. The plate I is connected to a source ofpositive voltage B, theplate being bypassed to ground by a large bypasscondenser ii. The auxiliary anode II is connected to ground through apath which includes load resistor 16, the latter being shunted by anintermediate frequency carrier by-pass condenser 1 ll. Auxiliary voltagedeveloped across resistor I0 is transmitted to any desired type of audiofrequency utilization network through the audio coupling condenser it Itis to be understood that the utilization network may comprise one ormore audio amplifiers followed by a reproducer.

The direct current voltage developed across load resistor N is employedfor automatic gain control of the signal transmission tubes prior to thedriver tube 1. Thus, lead I9 is connected to the signal grid ofamplifier 3, as well as to the signal grids of tubes prior to amplifier3. The usual pulsating voltage filter network is included in the lead20; the latter is designated by the letters AVC to automatic volumecontrol connection. The function of connection i9 is to decrease thegain of each signal amplifier as the carrier amplitude increases; inthis way the carrier amplitude at the detector input circuit ismaintained substantially uniform regardless of a wide range of signalcarrier amplitude variation at the signal collector.

With the arrangement shown full gain and selectivity are secured fromthe driver tube and from circuits 5, 6. The same amount of radiofrequency voltage appearing across circuit G also appears across circuit|3-|Z. The triode 9-3-|ii is degenerative for the intermediate frequencycarrier. The radio frequency voltage developed across tuned cathodecircuit |.3-|2 is applied to the'diode anode I; the rectified currentflows through resistor It. The tuned circuit |3-|2 may in itself be ofinfinite impedance, but looking back into the triode 9-8-40 it sees animpedance which is equal to the plate resistance divided by mu plus. 1.This impedance is very low; for example, it can be as low as 500 ohms.In other words the diode 8-H looks into a 500 ohm impedance. For thisreasonv the load resistor l5 may be chosen to have a small resistancemagnitude; hence, load l6 can be chosen for 100% modulation capabilitywithout regard to loading of tuned input circuits.

Since the diode 8--|I only operates on the positive half cycles, thedriver triode need only supply half cycles to the diode. For this reasonthe signal grid '9 is biased substantially to cut off. Current will thenflow through diode 5-8 on. the positive half cycles of'waves applied tosignal grid 9.. This permits driver triode 9 -8-4 9.

denote that it is the to handle signals of larger magnitude. It' will,

therefore, be seen that actually a classB amplifier for the carrier.

driver triode 9 -8-48 is degenerated work. The triode detector issimilar in action to the square law or power detector with the exceptionthat it is degenerative at the carrier. If circuit |3-|2 is tunedexactly to the carrier, as in Fig. l, the circuit is degenerative (100%)to the carrier. It may be expected that the triode detector in such caseis linear to the carrier, as

well as the audio. Very little carrier voltage will appear in the platecircuit; hence, a small by-pass condenser 22, about 100 mmf., can beconnected across plate resistor 2!. The carrier voltage which appears inthe detector plate circuit will depend on the ratio of resistor 2| tothe impedance of tuned. circuitv |3--|2. If desired, coil i2 may beemployed without use of the tuning condenser l3. across it enough.degenerative volt-age to linearize the detection characteristic forsmall amplitude signals; for strong signals the 100% degeneration is notrequired to linearize the characteristic since the power detector islinear for such high amplitude signals. Further, there would'besufficient voltage developed across the untuned cathode. impedance tosupply the diode rectifier and produce good control action.

If the tunedcircuit (|3-|2) impedance is high (high Q coil) it mayaugment the plate resistance to sucha high value that the output acrossthe plate load 2| is very small, and almost zero. To prevent this thetuned circuit |3-|2 may be shunted by a resistor 30... Quite a low valueof resistance for 30 may be used without reducing the voltage applied tothe diode. This follows from the fact that the diode looks into an impedance of say 500 ohms. A value of 50,000 ohms for resistor 30 wouldhave small shunting eiiect on the 500 ohms impedance. If desired, atuned circuit 40 can be placed in the cathode circuit of amplifier 3 tocause degeneration.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled inthe art thatmy inventionv is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention, as set forth in the appendedclaims.

What I claim is:

1. In a signal receptionnetwork, an electron ing resonated to saidcarrier frequency, means for maintaining said output electrode at apositive potential, an auxiliary anode operatively associated with saidcathode and providing a diode for rectifying carrier signal currentdevelopedin said second tuned circuit, a load resistor connected betweensaid anode and said point of fixedpotential, and means, for derivingfrom. the

The untuned coil may build up rectified current flowingthrough saidload. resistor a direct current voltage whose magnitude is proportionalto the carrier amplitude.

2. In a signal reception network, an electron discharge device includingat least a cathode, a signal grid and an output electrode, a source ofsignals coupled to the signal grid, said source including a tunedcircuit resonant to the operating signal carrier frequency, a secondtuned circuit connected between the cathode and a point of fixedpotential, said second tuned circuit being resonated to said carrierfrequency, means for maintaining said output electrode at a positivepotential, an auxiliary anode operatively associated with said cathodeand providing a diode for rectifying carrier signal current developed insaid second tuned circuit, a load resistor connected between said anodeand said point'of fixed potential, means for deriving from across saidload resistor a direct current voltage whose magnitude is proportionalto the carrier amplitude, and means for biasing said signal gridsubstantially to space current cut-ofi.

3. In a signal reception network, an electron discharge device includingat least a cathode, a

signal grid and an output electrode, a source of signals coupled to thesignal grid, said source including a tuned circuit resonant to theoperating signal carrier frequency, a second tuned circuit connectedbetween the cathode and a point of fixed potential, said second tunedcircuit being resonated to said carrier frequency, means for maintainingsaid output electrode at a positive potential, an auxiliary anodeoperatively associated with said cathode and providing a diode,

a load resistor connected between said anode and said point of fixedpotential, means for deriving from across said load resistor a directcurrent volt-age whose magnitude is proportional to the carrieramplitude, at second load resistor connected to said output electrode,and means for deriving from across the second load resistor a voltagerepresentative of the modulation on the signal carrier.

4. In a signal reception network, an electron discharge device includingat least a cathode, a

signal grid and an output electrode, a source of signals coupled to thesignal grid, said source including a tuned circuit resonant to theoperating signal carrier frequency, a second tuned circuit connectedbetween the cathode and a point of fixed potential, said second tunedcircuit being resonated to said carrier frequency, means for maintainingsaid output electrode at a positive potential, an auxiliary anodeoperatively associated with said cathode and providing a diode, a loadresistor connected between said anode and said point of fixed potential,means for deriving from across said load resistor a direct currentvoltage whose magnitude is proportional to the carrier amplitude, saidsecond tuned circuit developing carrier voltage thereacross which isimpressed on said signal grid in degenerative phase, means for derivingfrom across said load resistor audio voltage, and means for biasing saidsignal grid to cut-off.

5. In combination, in a signal detector network, a tube including atleast a cathode, a plate and a signal grid therebetween, and at leastone auxiliary anode adjacent the cathode to receive an electron streamtherefrom which is independent of the electron stream flowing to saidgrid and plate, a signal carrier input circuit connected between thesignal grid and a point of relatively fixed potential, a tuned circuitconnected between the cathode and said point of fixed potential, saidtuned circuit developing carrier voltage thereacross which is impressedon the signal grid in degenerative phase, a load resistor connected tosaid plate for developing audio voltage-thereacross, and a second loadresistor connecting said auxiliary anode to said point of fixedpotential, and means for deriving a direct current Voltage from acrosssaid second resistor which is proportional to the carrier amplitude.

6. In combination, in a signal detector network, a tube including atleast a cathode, a plate and a signal grid therebetween, and at leastone auxiliary anode adjacent the cathode to receive an electron streamtherefrom which is independent of the electron stream flowing to saidgrid and plate, a signal carrier input circuit connected between thesignal grid and a point of relatively fixed potential, a tuned circuitconnected between the cathode and said point of fixed potential, saidtuned circuit developing carrier voltage thereacross which is impressedon the signal grid in degenerative phase, a load resistor connected tosaid plate for developing audio voltage thereacross, and a second loadresistor connecting said auxiliary anode to said point of fixedpotential, means for deriving a direct current voltage from across saidsecond resistor whichis proportional to the carrier amplitude, and saidtuned circuit being resonated to the carrier, and means for normallybiasing said signal grid to cut-off.

7. In combination, in a signal detector network, a tube including atleast a cathode, a plate and a signal grid therebetween, and at leastone auxiliary anode adjacent the cathode to receive an electron streamtherefrom which is independent of the electron stream flowing to saidgrid and plate, a signal carrier input circuit connected between thesignal grid and a point of relatively fixed potential, a reactiveimpedance connected between the cathode and said point of fixedpotential, said reactive impedance developing carrier voltagethereacross which is impressed on the signal grid in degenerative phase,a load resistor connected to said plate for developing audio voltagethereacross, and a second load resistor connecting said auxiliary anodeto said point of fixed potential, means for deriving a direct currentvoltage from across said second resistor which is proportional to thecarrier amplitude.

8. In combination with a triode detector which is provided with acarrier-tuned input circuit, means in the space current path of thedetector for developing carrier voltage which is impressed upon thedetector signal grid in degenerative phase, a carrier rectifier circuitcomprising a diode whose cathode is the cathode of said triode and whoseanode is an auxiliary anode disposed adjacent the cathode, a loadresistor in circuit with the space current path of the diode, carriervoltage developed across said means being impressed on said diode, andmeans for deriving the direct current voltage developed across said loadresistor.

9. In a signal reception network of the type provided with a tube havingat least a cathode, signal input electrode and signal output elec trode,a signal-tuned input circuit coupled to the signal input electrode andcathode, means applying a positive potential to said output electrode;the improvement which comprises a reactive impedance in the spacecurrent path of said tube for developing signal voltage which isimpressed on said signal input electrode in degenerative voltage inputelement, a load impedance in said rectifier circuit for developing auni-directional voltage thereacross which is derived from rectifiedsignal voltage, and means for biasing said signal input electrodesufiiciently negative to permit said tube to function as a class Bamplifier whereby it is adapted to handle signals of relatively largemagnitude.

10. In a signal reception network of the type provided with a tubehaving at least a cathode, signal input electrode and signal outputelectrode, a signal-tuned input circuit coupled to the signal inputelectrode and cathode, means applying a positive potential to saidoutput electrode; the improvement which comprises a reactive impedancein the space current path of said tube for developing signal voltagewhich is impressed on said signal input electrode in degenerative phase,a signal rectifier circuit including said reactive impedance as thesignal voltage input element, a load impedance in said rectifier circuitfor developing a uni-directional voltage thereaci'oss which is derivedfrom rectified signal voltage, and said rectifier circuit including adiode whose elements are said cathode and an auxiliary anode adjacentsaid cathode within said tube.

11. In a signal reception network of the type provided with a tubehaving at least a'cathode, signal input electrode and signal outputelectrode, a signal-tuned input circuit coupled to the signal inputelectrode and cathode, means applying a positive potential to saidoutput electrode; the improvement which comprises a reactive impedancein the space current path of said tube for developing signal voltagewhich is impressed on said signal input electrode in degenerative phase,a signal rectifier circuit including said reactive impedance as thesignal voltage input element, and a load impedance in said rectifiercircuit for developing a uni-directional voltage thereacross which isderived from rectified signal voltage, said reactive impedanceconsisting of a resonant circuit which is tuned to the frequency of saidinput circuit.

SEYMOUR HUNT.

